1. Field of the Invention
The invention relates to a device and a method for detecting motor vehicles and their approach angles by means of passive or active transponders which are provided in motor vehicles, which can be triggered by a transmission and receiving device to transfer information stored in the transponders.
2. Description of the Related Art
The background to the present invention is that modern passenger assistance systems are increasingly also being used for accident prevention purposes, wherein they detect objects in the area surrounding the motor vehicle and predict possible accident trajectories. These systems can however only detect with great difficulty whether the detected object is a motor vehicle or another obstacle. The motor vehicle type (lorry, motorbike, car etc.) can only be determined with complex sensors. For detection, highly sophisticated detection algorithms are necessary which are in general based on an image evaluation using video data.
DE 693 17 266 T2, which is incorporated by reference, discloses a method for monitoring road traffic which records the presence of motor vehicles moving in front and their dynamic conditions, and evaluates this in a processor, as well as recording transfer time windows and transferring the message to motor vehicles behind during the recorded time window. As a result, the motor vehicle is operated as a moving station in order to record in real time both its own dynamic conditions as well as those of the other motor vehicles in front of the motor vehicle, and to transmit them onwards. This system is highly complex, however, and requires the coordination in time of diverse information in a chain of several transmitters and receivers. Due to the determination of suitable transfer time windows, a great deal of time is lost in hazardous situations until the information is forwarded to other motor vehicles. Furthermore, all motor vehicles must be equipped with suitable and synchronised transmitters and receivers. This makes it significantly more difficult for the system to be implemented in practise, and entails the risk that many motor vehicles will not be equipped with the suitable, expensive system.
DE 44 11 125 C2, which is incorporated by reference, describes an information system consisting of several passive transponders, in which messages are stored respectively, and of at least one transceiver device which is installed in a motor vehicle for the activation of the transponder and to receive messages sent from an activated transponder. The transceiver device transmits polarised emission energy to the transponder which then converts the emission energy received in order to read data from the storage device and to created modulated and coded messages, as well as to return these messages back to the device in the form of horizontally or vertically polarised radio waves, in order to be able to suppress interference emission due to diffuse reflection from fences, bushes, buildings etc. which are also received as (non-polarised) signals. In order for a moving motor vehicle to continue to receive information from the transponder which has been reflected due to the energy emission, an emission field is generated by the transceiver device which is preferably club-shaped. However, with this system, it is not possible to provide information about changing values, for example the presence of other motor vehicles.